In many manufacturing plants or other facilities, such as papermills, where large pumps are run continuously to convey a process liquid for a mixing process, cooling and lubricating mediums such as water or oil often are used to cool and lubricate the seals or bearings surrounding the drive shafts of the pumps. The heat generated due to friction between the drive shaft and the sides of the impeller housing and the high temperature to which the process liquid is generally heated can cause the failure of the seals or bearings, which can result in expensive pump down time.
When the seal fails, the process liquid can leak out of the apparatus or the cooling water will leak in, mixing with and contaminating the process liquid. Such leaks waste water and waste energy as the mixing of cooling water with the process liquid lowers the temperature of the process liquid, requiring additional energy and thus additional expense to maintain the temperature of the process liquid at the proper processing level. It therefore is highly desirable to detect a breach of the seal of a pump as early as possible so that the seal can be repaired or replaced, thereby restoring the efficiency of the process and prolonging the life of the seal.
In general, flow meters are used to monitor and regulate flow of a fluid medium such as sealing water about a pump seal. Flow meters measure the pressure and rate of flow of the sealing water thereby to provide an indication of the integrity of the pump seal. If the flow increases and pressure drops, it is an indication of a leak of the process liquid out of the process. If the flow drops and the pressure rises, it is an indication that the sealing water is leaking into the process liquid. Thus, flow meters provide an indication of the incipient failure of the pump seal. In general, there are several types of flow meters used to measure the flow amount of liquids or gasses depending on the application. Typically, most conventional flow meters have a conical metering channel into which the liquid flows from the narrow end of the cone and leaves at the broader end of the cone, and a float mounted in the cone. The position of the float changes in accordance with the volume of the flow through the metering channel and provides an indication as to the flow volume. Other types of conventional flow meters include a cylindrical metering channel having a float located therein indicating the volume of flow through the metering channel.
The main problem that occurs with most conventional flow meters is that over time the readability of the meter becomes diminished by collected dirt and debris. The water used to cool and lubricate pump seals in most processing plants is generally waste water which has a considerable amount of dirt and other impurities. This dirt and grime tends to accumulate within the flow tube of the flow meter. The accumulation of dirt consequently clouds the flow tube and restricts the flow through the flow tube, making it difficult for the float to move to the correct indicator point and making it difficult to read and take accurate measurements of the rate of the flow through the system.
Accordingly, flow meters having a cleaning function for cleaning the flow tube thereof have been developed. Such flow meters generally include a movable float mounted on a conically shaped rod extending along the length of the flow tube. However, the cleaning function of these conventional flow meters generally is limited only to a section or portion of the flow tube between the zero indicator and the float which gives the current flow indication. Consequently, there is a portion of the flow tube from which accumulated dirt and grime is not cleaned.
For example, Finnish Patent No. 53042 discloses a conventional flow meter having a conical flow tube or channel that includes a brush positioned below the float tube and which is moveable along a portion of the length of the flow tube between the inlet end and the float thereon. The use of this brush to clean the flow tube is, however, somewhat inefficient as the brush must be turned as it is moved along the length of the flow tube for proper cleaning of the flow tube, and the brush is prevented from reaching the upper regions of the flow tube by the position of the float on top of the brush. Further, with the brush in its cleaning position, the flow of liquid through the flow tube is substantially disrupted, so that the flow meter cannot function to indicate the volume of flow of the liquid through the meter during cleaning. Additionally, Finnish Patent No. 61759 discloses a variable area flow meter having a cleaning function that is accomplished by the momentary reversal of the direction of the flow of the liquid through the flow meter so as to move the float from the metering position to a zero position and back as the normal flow resumes. The problem with such device is that the movement of the float only cleans that part of the flow tube that is between the measured position of the float and the zero value. As a result, the remainder of the flow tube will remain cloudy and will continue to accumulate dirt and grime to the point where the flow tube will become unusable and thus will destroy the function of the flow meter, requiring the flow meter to be disassembled and cleaned.
An additional problem that is common to conventional flow meters is that during the cleaning operation the flow of the liquid through the flow meter either must be completely stopped or is substantially disrupted, as taught by Finnish Patent No. 61759, by a reversal of the flow or the insertion of a brush that engages the sides of the flow meter. Such disturbances in the flow of the liquid through the flow meter has serious consequences for the equipment being cooled by the liquid flowing through the flow meter, possibly leading to damage and failure of such equipment due to a disruption in the flow of cooling water to the seals thereof.
Additionally, many conventional flow meters now are equipped with low flow alarms that are triggered if the flow decreases under a preset limit. Generally, such alarms are connected to the process control system so that when the alarm is triggered, the entire process is shut down. As a consequence, when conventional flow meters, such as those discussed above, are cleaned, the floats tend to move past the lower limit set point of the alarms triggering the alarm and shutting down the system. To avoid false alarms, such as when the flow meter is being cleaned, the control systems for such flow meters require a delay or bypass circuit that will switch on while cleaning. However, in spite of such delays and spite of these delay circuits, false alarms still occur frequently as sometimes it is necessary to perform multiple cleaning operations to substantially completely clean the flow meter of accumulated dirt and grime therein. Thus, the cleaning function performed by conventional flow meters generally is incomplete and causes disruptions in the system that can lead to system shutdown or other problems.
Therefore, it can be seen that a need exists for a variable area flow meter which has a self-cleaning function that quickly and completely cleans the flow tube thereof of any accumulated dirt and debris without substantially disrupting the flow of the fluid medium therethrough. Accordingly, it is the provision of a flow meter with an improved self cleaning function to which the present invention is primarily directed.